The present invention relates generally to device fabrication and, in particular, to the fabrication of metal-insulator-metal (MIM) capacitive structures.
Various capacitive structures are used as electronic elements in integrated circuits. Such structures include, for example, metal-oxide-semiconductor (MOS) capacitors, p-n junction capacitors and metal-insulator-metal (MIM) capacitors. For some applications, MIM capacitors can provide certain advantages over MOS and p-n junction capacitors because the frequency characteristics of MOS and p-n junction capacitors may be restricted as a result of depletion layers that form in the semiconductor electrodes. An MIM capacitor can exhibit improved frequency and temperature characteristics. Furthermore, MIM capacitors are formed in the metal interconnect layers, thereby reducing CMOS transistor process integration interactions or complications. Additionally, the topology of the MIM capacitor simplifies planarization processes.
A MIM capacitor includes an insulating layer, such as a dielectric, disposed between lower and upper electrodes. Typically, after formation of the lower MIM capacitor electrode in a first chamber, the wafer is transferred to another chamber or furnace where the insulating layer is deposited. The wafer subsequently is returned to the first chamber or yet a third chamber for deposition of the upper electrode. Titanium nitride (TiN) is sometimes used as the material for the capacitor electrodes.
One difficulty that is encountered during such a fabrication process results from the exposure of the wafer to an ambient containing oxygen when the wafer is transferred from the first chamber to another chamber or furnace for deposition of the insulating layer. As a result of exposure to the oxygen, a thin porous metal oxide film forms on the upper surface of the lower TiN electrode. The presence of the thin porous metal oxide film at the interface between the TiN and insulating layer can allow charge to become fixed or trapped at the interface. Moreover, if the porous metal oxide film is present only at the interface of one electrode, the capacitive structure can exhibit undesired hysteresis affects as the capacitor charges and discharges. Accordingly, improvements in the fabrication of MIM capacitive structures are desirable.